A Diels–Alder-Based Total Synthesis of (−)-Kainic Acid

An efficient synthesis of (−)-kainic acid, through a high-pressure-promoted Diels–Alder cycloaddition of a vinylogous malonate derived from 4-hydroxyproline, is described. The bicyclic adduct could be converted into the natural product with complete stereocontrol

First Donor-Stabilized Complexes of Manganese(II) with Disubstituted diphenyldithiophosphates: synthesis, characterization, biological, and X-ray Analysis

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Aggregation of Donor Base Stabilized 2-Thienyllithium in a Single Crystal and in Solution: Distances from X-ray Diffraction and the Nuclear Overhauser Effect

Various 2-thienyllithium derivatives were investigated in the solid state by X-ray diffraction and in solution by 2D NMR experiments. The determined structures of [(Et₂O)­Li­(C₄H₃S)]₄ (<b>1</b>), [(THF)₂Li­(C₄H₃S)]₂ (<b>2</b>), [(DME)­Li­(C₄H₃S)]₂ (<b>3</b>), [(TMEDA)­Li­(C₄H₃S)]₂ (<b>4</b>), and [(PMDETA)­Li­(C₄H₃S)] (<b>5</b>) (DME = 1,2-dimethoxyethane, TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylene-1,2-diamine, and PMDETA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>″,<i>N</i>″-pentamethyldiethylenetriamine) were solved in nondonating toluene and provide firm ground for diffusion-ordered NMR spectroscopy as well as heteronuclear Overhauser enhancement NMR spectroscopy. The distance relation of nuclear Overhauser effects with a factor of <i>r</i>^–6 is employed to gain further insight into the aggregation degree of <b>1</b>–<b>5</b> in solution. Comparison of the slope provided by the linear region of the buildup curves and of the ∑<i>r</i>^–6 calculated distances from the crystal structures offers a handle to judge the structure retention versus conversion in solution. The structures of <b>3</b>–<b>5</b> are maintained in toluene solution. The data of <b>2</b>, however, indicate a partial dissociation or a rapid exchange between the vertices of a tetrameric core and free THF molecules. Auxiliary exchange spectroscopy investigations showed that the signals of the nitrogen donor base containing compounds <b>4</b> and <b>5</b> exchange with the signals of nonlithiated thiophene. This is explained by exchange of the deuterium by a hydrogen atom via lithiation of toluene molecules